1. Field of the Invention
The present invention relates to the treatment of cardiac conditions, and more particularly, to apparatus and methods for controlling depth of injection into myocardial tissue.
2. Description of Related Art
Heart failure (“HF”) is generally defined as a change in the pumping function of the heart accompanied by typical signs or symptoms. Heart failure is a progressive disorder whereby the hemodynamic and symptomatic states of the patient worsen over time despite the absence of clinically apparent adverse events. The symptomatic deterioration is often accompanied by progressive left ventricular (“LV”) chamber remodeling.
Preventing or reversing remodeling has emerged as desirable in the treatment of cardiomyopathy. Cardiomyopathy is a general term for disease of heart muscle regardless of the underlying etiology, which may be, for example, ischemic, hypertensive, dilated, hypertrophic, infiltrative, restrictive, viral, postpartum, valvular, or idiopathic. Cardomyopathy typically results in heart failure.
Myocardial infarction (“MI”) is a medical emergency in which some of the heart's blood supply is suddenly and severely reduced or cut off, causing the myocardium to die because it is deprived of its oxygen supply. A myocardial infarction may progressively advance into heart failure. Scar tissue formation and aneurysmal thinning of the infarct region often occur in patients who survive myocardial infarctions. It is believed that the death of cardiomyocytes results in negative left ventricular (LV) remodeling which leads to increased wall stress in the remaining viable myocardium. This process results in a sequence of molecular, cellular, and physiological responses which lead to LV dilation. Negative LV remodeling is generally considered an independent contributor to the progression of heart failure.
Mitral regurgitation (“MR”) is incompetency of the mitral valve causing flow from the left ventricle (LV) into the left atrium during systole. Common causes include mitral valve prolapse, ischemic papillary muscle dysfunction, rheumatic fever, and annular dilation secondary to LV systolic dysfunction and dilation. MR may lead to heart failure.
At the present time, the most effective treatment for patients in end-stage heart failure is heart transplantation. However, given the chronic shortage of donor hearts, alternate strategies are needed to improve the lives of those with heart failure. Moreover, transplantation is not the most suitable treatment option for patients with milder forms of the disease. Other treatment approaches include the delivery of drugs to the site of action through the bloodstream, and the injection of cells into ischemic myocardium to improve cardiac function. An example of an approach for treating cardiovascular problems with an intramyocardial scaffold is disclosed in United States Patent Application Publication No. 2005/0271631, published Dec. 8, 2005 in the name of Lee et al. and entitled “Material compositions and related systems and methods for treating cardiac conditions.”
One of the approaches described in the Lee Published Patent Application uses a needle to inject the material that forms the intramyocardial scaffold into the myocardium. Care should be taken to ensure that the needle use for the injection is placed at an appropriate depth in the myocardium.